Systems for measuring the intra-arterial blood pressure of a patient can be subdivided into two main groups--those which invade the arterial wall to access blood pressure and those which use noninvasive techniques. Initially, the most accurate blood pressure measurements were achievable only by way of invasive methods. One common invasive method involves inserting a fluid filled catheter into the patient's artery.
While invasive methods provide for accurate blood pressure measurements, the associated risk of infection and potential for complications, in many cases, outweigh the advantages in using invasive methods. Because of these risks associated with invasive methods, a noninvasive method, known as the Korotkoff method is widely used.
The Korotkoff method is known as an auscultatory method because it uses the characteristic sound made as the blood flows through the artery to mark the points of highest (systolic) and lowest (diastolic) blood pressure. Although the Korotkoff method is noninvasive, it only provides a measurement of the highest pressure and the lowest pressure along the continuous pressure wave. While systolic and diastolic pressure are sufficient for accurate diagnosis in many instances, there are many applications in which it is desirable to monitor and utilize the entire characteristic curve of the blood pressure wave. In these applications, the Korotkoff method simply is incapable of providing ample information. In addition to this limitation of the Korotkoff method, it necessitates the temporary occlusion of the artery in which blood pressure is being monitored. While arterial occlusion is not prohibitive in many applications, there are occasions where the patient's blood pressure must be monitored continuously (such as when undergoing surgery) and accordingly, the prohibiting of blood flow, even on a temporary basis, is undesirable.
Because of the above-mentioned risks involved with invasive blood pressure measurement, and the shortcomings of the Korotkoff method, extensive investigation has been conducted in the area of continuous, noninvasive blood pressure monitoring and recording. Some of these noninvasive techniques make use of tonometric principles which take advantage of the fact that as blood pressure flows through the arterial vessel, forces are transmitted through the artery wall and through the surrounding arterial tissue and are accessible for monitoring at the surface of the tissue. Because the tonometric method of measuring blood pressure is noninvasive, it is used without the risks associated with invasive techniques. Furthermore, in addition to being more accurate than the Korotkoff method discussed above, it has the capability of reproducing the entire blood pressure wave form, as opposed to only the limited systolic and diastolic pressure points provided by the Korotkoff method.
Because the accuracy of tonometric measurements depends heavily upon the method and apparatus used to place and maintain the sensor against the tissue overlying the artery of interest, several apparatuses have been specifically developed for this purpose. For example, U.S. Pat. No. 4,784,152 issued to Shinoda, et al. on Nov. 15, 1988 discloses a sensor positioning device which is capable of moving a contact sensor relative to and along the surface of a patients body tissue. A pressing device is provided for moving each contact element relative to the main frame, in a direction toward the tissue, for forcing each sensor against the tissue. Likewise, U.S. Pat. No. 4,947,855 issued to Yokoe, et al. on Aug. 14, 1990 discloses a blood pressure measuring apparatus having a housing detachably set on a body surface of a subject. A pressure sensor is accommodated in the housing such that the pressure sensor is opposed to the body surface when the housing is set on the body surface, the pressure sensor being pressed against the body surface so as to detect pulse waves produced from an arterial vessel of the subject. Also, in U.S. Pat. No. 4,966,156 issued to Perry, et al., a pressurization system for continuous blood pressure monitoring is disclosed comprising a dual chamber compression apparatus and switching mechanism, both of which are engaged to a servo motor drive mechanism. The drive mechanism simultaneously controls the compression apparatus and the switching mechanism thereby coordinating flow of air from the compression chamber to the pressurizable chamber within the transducer.
It can be seen, in conjunction with the above-mentioned patents, that they possess several drawbacks. Firstly, they do not possess the means for releasing the pressure applied by the pressure sensing head in the event that the pressure applied becomes excessive (such as in a malfunction condition). Secondly, the construction of the above-discussed systems is not modular and accordingly, the majority of its components are not field serviceable. Thirdly, it is evident from the above systems, that because they directly contact the skin of the wearer, any contaminants thereon is transferred to the sensing head thereby contaminating the head, and possibly being transferred to a subsequent wearer. Lastly, by way of general observation, the above-discussed systems are generally bulky, and accordingly, are cumbersome to use and operate. Moreover, the above systems are designed to be universally applicable for either right or left wrist usage. Because they are designed with this universality in mind, they are unable to take advantage of specific wrist characteristics when, properly taken advantage of, can provide a more stable platform to thereby engage and operate the tissue stress transducer.
Thus, it is desirable to provide a wrist mount apparatus for use in blood pressure tonometry wherein various wrist characteristics are taken advantage of to provide a single sensor which can universally adapt to the right or left wrist and accordingly, provide a secure platform to thereby mount a tissue stress sensor upon.
It is also an object of this invention to provide a force overload release system whereby the risk of damage to the tissue of a wearer is minimized should the device fail and attempt to apply excessive force to the wearers wrist area.
It is also an object of this invention to provide a quick disconnect system whereby the tissue stress sensor may be quickly removed from the wrist mount apparatus thereby making the entire assembly less costly to service and also allowing the wrist mount apparatus to be field serviceable and even disposable.
It is still an additional feature of this invention to provide a wrist mount apparatus which minimizes the risk that contaminants will be passed from wearer to wearer or from a wearers wrist to the tissue stress sensor head.
Yet still it is an object of the present invention to provide a wrist mount apparatus which assists an operator in quickly and easily locating an artery of interest while also acting to stabilize the artery thereby reducing its tendency to move or roll.